A wide variety of luminescent rare-earth-containing compositions are known in the art. Both inorganic and organo-metallic luminescent rare-earth-containing compositions have been identified.
Rare-earth metal ions absorb ultraviolet light and luminesce in the visible or the infrared. When a rare-earth is complexed with certain aryl organic ligands luminescence quantum yield of the rare-earth is enhanced by the broad band absorbance of the organic moiety in the ultraviolet spectrum which can efficiently transfer energy non-radiatively to the emitting rare-earth ion.
Mathur et al., Synth. React. Inorg. Met.-Org. Chem. 11(3), 231-244 (1981) discloses lanthamide chelates wherein the associated ligands are represented by the formula R1NHC(O)R2 wherein R1 is phenyl, chloro-phenyl, or nitro-phenyl, and R2 is methyl or phenyl with the proviso that when R2 is phenyl, R1 must also be unsubstituted phenyl. The lanthamide chelates disclosed therein were employed for infrared spectroscopic studies.
Many types of ligands are known in the art for use in forming chelates with rare-earth metals, and, even more generally, with transition metals. Despite this plethora of compositions, there is a continuing need for rare-earth chelates that luminesce with high quantum yield, particularly in the visible part of the spectrum, and that exhibit thermal stability for good processibility and extended use temperatures.